OLED, as a new type of display technology, has unique advantages such as self-illumination, wide viewing angle, low power consumption, high efficiency, thin, rich colors, fast response, extensive application temperature, low drive voltage, used to make flexible, bendable and transparent display panel and environmental friendliness, etc. Therefore, OLED technology can be applied to flat panel displays and new generation of lighting, or can be used as backlight of LCD.
OLED is a device made through spin-coating or depositing a layer of organic material between two metal electrodes. A classic three-layer OLED comprises a hole transport layer, a light emitting layer and an electron transport layer. The holes generating from the anode through the hole transport layer and the electrons generating from the cathode through the electron transport layer combine to form excitons in the light emitting layer, emitting light. By changing the material of the light emitting layer, the OLED can emit red light, green light and blue light, and OLED can also emit the white light through material matching in the light emitting layer.
However, the applications of existing OLEDs are restricted by low efficiency and short service life, therefore, these constraints must be avoided. Lowering the energy barrier between the hole injecting/transport material and the light emitting material and improving the thermal stability of hole transport material can facilitate to improve the efficiency and enhance the life of OLEDs; besides, due to poor solubility of small molecule hole-injecting/transport material, the device can be prepared by depositing, which is not conducive to its commercialized use. Therefore, the large-scale applications of devices can be improved by developing the materials with high hole mobility, to achieve the spin-coating and ink-jet printing.
The existing hole injecting material copper phthalocyanine (CuPc) is not environmentally friendly due to its slow degradation and high energy consumption for preparation. The common hole transport materials TPD and NPB have good hole mobility, 1.0*10−3 and 5.1*10−4 cm2V−1S−1 respectively, but their glass transition temperatures are 65° C. and 98° C. respectively, and their stability cannot meet application requirements of OLED. Thus, it is necessary to develop efficient and stable OEL material, to produce highly efficient and stable OLEDs.